The present invention relates to a vehicle steering or suspension system, and particularly relates to a boot seal for sealing a movable joint in a vehicle steering or suspension system.
Boot seals are used to protect the bearings in joints between relatively movable parts of vehicle steering and suspension systems. The boot seals are typically formed of a thermoplastic or thermosetting elastomer. Examples of prior art elastomers are neoprene rubber, a blend of ethylene-propylene rubber and polypropylene marketed by Monsanto Company of St. Louis, Mo. under the trademark SANTOPRENE, and HYTREL polyester marketed by E.I. DuPont de Nemours Co.
The boot seals are typically blow molded into the configuration in which they are to be installed, and are snapped into place in an interference fit which is secured by metal clips.
Boot seal failure can be caused by fatigue, punctures, cuts or tears, and abrasive wear. Boot seal failures are a common cause of joint failure. If a boot seal fails, water and dirt can get into the joint, and/or grease can leak out. It is desirable to increase the resistance of boot seals to failure.
The present invention is directed to a process for making a plastic tube having a variable diameter. The process comprises the following steps. A plastic is obtained. The plastic is fed into an extruder die. The plastic is extruded as a tubular molten plastic stream into a mold cavity having an inside diameter greater than the diameter of the tubular molten plastic stream. The mold cavity inside diameter varies longitudinally along the length of the mold cavity. The tubular molten stream is vacuum expanded radially against the mold cavity inner wall. The wall thickness of the tubular molten plastic stream is varied during extrusion at locations longitudinally along the stream.